A schematic cross sectional view of a conventional thin film capacitor is shown in FIG. 1. After forming a metal film on a formed substrate 1 such as by a sputtering device, a resist is formed through a conventional photolithograph process and a lower electrode 2 is formed such as by dry etching. Thereafter, a dielectric material is formed by sputtering or CVD, then a dielectric layer 3 is formed through photolithography. Further, an upper electrode 4 is formed in the same manner as in the formation of the lower electrode. Through the above processes a conventional thin film capacitor was manufactured. Further, JP-A-9-289611 discloses a thin film capacitor in which, after forming a sidewall face inclined at a gentle angle at the edge portion of a lower electrode as shown in FIG. 2, a dielectric layer 3 and an upper electrode 4 are formed. As the method of forming the sidewall face at the lower electrode edge, a metal thin film is formed on a substrate. A resist is formed on the metal thin film, and then ion beams are irradiated onto the metal thin film at a predetermined angle θ.
In the conventional capacitor as shown in FIG. 1, the film thickness B of the dielectric layer at the step portion of the lower electrode edge portion is thinner than the film thickness A over the lower electrode. As a result, the distance between the upper and lower electrodes is shortened. For this reason, dielectric breakdown voltage is reduced and shorting between the electrodes tends to be caused due to factors such as dielectric layer defects. Further, in the case of a capacitor as shown in FIG. 2, since the inclination is formed only in a predetermined direction, when a plurality of capacitors are formed on a common substrate, the leading direction of lead wires of the upper electrode is limited to a single direction. Therefore, the circuit design is greatly restricted.
JP-A-4-336530 discloses a liquid crystal display in which a dielectric film insulating between the edge face of a lower electrode for a holding capacitor and a transparent pixel electrode is formed thicker than a dielectric film constituting the holding capacitor. However, in the capacitor used for the liquid crystal display, the thickness of the dielectric film is thin, so the above problem never happens.
An object of the present invention is to provide a highly reliable thin film capacitor, which prevents shorting between the electrodes and reduction of the dielectric breakdown voltage of the thin film capacitor elements and reduces the defects rate thereof.
Another object of the present invention is to provide a low defects rate as well as highly reliable electronic circuit incorporating such a capacitor.